Abstract

For understanding the physics of energetic particles, the deuterium experimental campaigns started in Large Helical Device (LHD) from March 2017. To investigate the behavior of energetic particles, a Fast-ion D Alpha (FIDA) diagnostic was installed on the LHD. In the FIDA diagnostic, the Doppler-shifted D alpha light from fast-neutrals are utilized as signals of energetic particles, where these fast-neutrals are produced by the charge exchange process between fast-ions in the plasma and actively injected neutrals by neutral beam (NB). The advantages of the FIDA diagnostic are the velocity and the spatially resolved measurement of fast-ions at the crossing point between its line of sight (LOS) and the incident line of NB. The most recent FIDASIM is enhanced to simulate signals produced in three-dimensional magnetic configurations. The new version of FIDASIM uses the fast-ion distribution function produced by GNET as input to simulate FIDA signals at LHD. In order to validate the new version of the code, measurements of radial profiles of fast-ions using the FIDA diagnostic are performed in magnetohydrodynamic (MHD)-quiescent plasmas. The measured spectra are in good agreement with the theoretical prediction by 3D-supporting FIDASIM at the center of the plasma (R= 3.5 m∼3.7 m, reff/a99= −0.28∼0.05) on the LHD when the line averaged electron density is ne_avg < 1.23 × 1019 m−3. On the other hand, the measured spectra are in disagreement with the theoretical prediction by 3D-supporting FIDASIM at even the center of the plasma when the line averaged electron density is ne_avg ≥ 1.23 × 1019 m−3.

Highlights

  • A magnetic confinement fusion reactor requires the sustainment of a high-temperature and highdensity plasma by energetic alpha particles from fusion reactions

  • The measured spectra and the predicted spectra are in good agreement between 654 nm to 659 nm at all measurement positions; this indicates that the halo and injected beam emission are accurately modelled

  • The Fast-Ion D Alpha (FIDA) diagnostic results and the FIDASIM results are in good agreement in MHD-quiescent plasmas at the center of the plasma for co-injection

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Summary

Introduction

A magnetic confinement fusion reactor requires the sustainment of a high-temperature and highdensity plasma by energetic alpha particles from fusion reactions. It is important to understand the behavior of energetic particles (such as fast-ions provided by plasma heating devices and fusion reactions) in magnetic confinement devices. The study of energetic particle confinement has advanced in tokamak type devices [1], and is one of the main topics in ITER [2]. The energetic particle confinement study in helical devices is rapidly developing. In the past several years, the fast-ion confinement study in helical devices demonstrated the potential for alpha particle confinement [7,8,9].

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